1. Field of the Invention
The present invention relates to a copying apparatus.
2. Description of the Prior Art
In a copying apparatus with slit exposure method in which the original is scanned by relative movement thereof with respect to an optical system, the speed of the scanning exposure of the original has been a technical factor hindering the high-speed copying. In a same size copying with scanning exposure of the original in the forward movement of the optical system, the number of copies made per unit time can be approximately represented by the following equation: EQU N=V/(l.sub.0 +l.sub.p +l.sub.l)(1+1/n),
wherein
N: number of copies PA0 l.sub.0 : length of the original PA0 l.sub.p : distance of preliminary movement PA0 .sub.lr : distance to the reversing position, including exposure slit width PA0 l.sub.l : time loss for changing direction in movement, converting into distance PA0 V: peripheral speed of the photosensitive drum PA0 n: speed ratio of backward movement to forward movement.
Thus, for a copier capable of forming 40 copies of A4 size (210.times.279 mm) per minute, and for the parameters of l.sub.0 =210 mm, l.sub.p =40 mm, l.sub.r =10 mm, l.sub.l =10 mm and n=2 (reversing at a double speed), the peripheral speed of the photosensitive drum is given by: EQU V=270 mm.times.1.5.times.40 copies/60 sec=270 mm/sec
so that the scanning speed has to be 270 mm/sec in the forward movement and 540 mm/sec in the backward movement.
In this manner an increased number N of copies calls for an increased speed V, which however will result in drawbacks such as an image blur caused by the shock at the reversing of the optical system or the wear thereof, or additional mechanisms and costs for preventing such drawback. Particularly in a copier having an image reduction capability, the scanning speed has to be increased by the reciprocal of the linear reduction rate. As the peripheral speed of the photosensitive drum in the presence of such image reduction capability is usually determined in consideration of the scanning speed at such image reducing operation, the drum peripheral speed for the same-size copying most frequently used is inevitably reduced by the presence of such image reduction capability.
Also there is already known a copier with variable magnification capability, performing the copying operation by selecting either one of plural sheet storage stations such as plural sheet cassettes. Such copier is designed to stop the copying operation in case of absence of a copying sheet matching the copy size of a varied magnification, and is therefore unable to form a reduced image on a part of a larger sheet.
However if the selection of the sheet storage stations is made independently of the selection of the magnification, the copied image may unexpectedly overflow the selected copy sheet particularly when multiple magnifications are selectable.
Also in case a copying of a determined image magnification is urgently needed during a multiple copying operation of another image magnification, such urgent copying can be achieved by the operator by suitable data input to interrupt said multiple copying and to displace the lens system to obtain said determined magnification, and in such case, after said urgent copying, the operator is required to enter data to return the lens system to the original magnification for continuing the interrrupted copying, to select the original cassette and to set the number of remaining copies. These operations are as cumbersome as starting the copying operation from the beginning.
Also in the conventional copier with variable magnification, the change in image magnification is principally achieved by the change in lens position and in the length of optical path.
The lens displacement method requires precise mechanical positioning of the lens and the mirror in the optical path, and for this reason the lens and the mirror are mechanically linked and the lens position is precisely determined mechanically by a stopper. In order to detect the lens position for each image magnification there is proposed the use of a long sensor for activating the stopper and for detecting the lens position. However, due to insufficient accuracy of such sensor, it is often unable to identify if the lens is stopped at a correct position.
It is naturally possible to provide a sensor for activating the stopper and another sensor for position detection for each image mangification, but such method will require an increased number of sensors with complicated wirings.
There is also known a copier provided with sorter for collating copies, and further known is such copier capable of displaying a warning upon detection of sheet jamming in said sorter. However such warning is only given in the form of "sorter jamming" or "copier jamming" in response to respective detection, and is unsatisfactory for the operator in eliminating such jamming, despite of the increase in the number of displays.
Furthermore it is known to provide a sensor on the moving path of the reciprocating member of the optical system or the original carriage as registering means for synchronizing the original scanning with the copy sheet feeding thereby registering the image to be formed on the photosensitive drum with the position of the copy sheet.
Also in order to detect the position of the reciprocating member, there are provided plural reversing sensors for indicating the reversing positions of the optical system which are determined corresponding to the initial home positions of said system.
Also in a copier with variable magnification capability the magnification in the direction of original scanning is varied by changing the speed of the optical system, and for this reason the registering sensor has to be provided for each image magnification. However the presence of multiple sensors along the scanning path leads to undesirable effects such as a lowered reliability, complication in wirings and an elevated cost.
Also if the speed of the scanning system is high in the repetitive copying operation, said system tends to overrun the original home position and to collide against the stopper. Such drawback can be prevented by a brake, which however involves a complicated structure and an elevated cost. Also the apparatus becomes inevitably larger if the home position or the stopper is provided at a farther location.
Furthermore, the conventional p-type microcomputer is structured to release a low-level output signal upon resetting after the start of power supply, whereby an inverted-type driver circuit, for example a switching element composed of a Darlington transistor circuit, connected to said microcomputer for example for driving a paper feed plunger, is not turned on at said resetting, thus preventing the erroneous function of the process load connected thereto.
On the other hand the n-type microcomputer, though being preferred in permitting the same power supply and signal voltage as in the conventional TTL circuits, releases a high-level output at the resetting, thus erroneously turning on the driver circuit to cause undesirable operation of the process loads. Such erroneous operation may cause sudden large current in the circuit, thus activating the circuit breaker or eventually deteriorating or damaging the circuit components.
Also in case the microcomputer is activated for time measurement etc. before the main switch is turned on for power supply to various operation loads and the resetting of said microcomputer is conducted by the self-judgement of said microcomputer, the erroneous function of process load such as abnormal lighting of the halogen lamp may take place without being noticed by anyone, thus leading to a dangerous situtation.
Also in case of a structure in which the microcomputer initiates the program execution even before the main switch is turned on and there are provided two systems of power supply, for example one for displaying copy number, absence of copy paper etc. and the other for paper-feed plunger, at least one of which is used as common power source for said microcomputer, some process loads cannot be turned off by the main switch and have to be cut off by the control signal from said microcomputer. Consequently the function of certain process loads, for example the display of copy number, may still be going on by an erroneous function of the microcomputer even after the main switch is cut off.
Furthermore, in case there are employed plural microcomputers, for example one for copying control and another for display control, either one may exert wild control in case of an erroneous function of the other, for example producing excessive copies.
Particularly of a microcomputer for controlling power supply switches such as the main switch or door switches and controlling power supply to the process loads is in normal state while the other microcomputer is in malfunction, there may result a dangerous situation because of the power supply to the process loads while the overall control of the apparatus is disabled.
Furthermore, in the use of a so-called one-chip microcomputer having program memories, data memories, input/output ports and a processing unit on a single chip of semiconductor, the data transfer between microcomputers have to be made through input-output ports due to the absence of the data bus line connected to the exterior. However the multiple functions in recent copier with many process loads and display devices require an elevated number of input/output ports for data transfer, with complicated program or sequence for the control of operations and displays.
Also the completion of resetting or the normal function of the microcomputer, which is identified by the level at an output port of said microcomputer, may become unidentifiable bacause of a malfunction of said port.
Furthermore in the use of multiple microcomputers, the identificaiton of the turning on of the main switch, if executed individually, will require a port in each microcomputer exclusively for this purpose, thus wasting port in each microcomputer.
Also the key counter, designed for use in counting the copy number for example in each division, is made insertable into the apparatus, which is structured incapable of copying operation without said key counter. However after the copying operation is initiated with the inserted key counter, the operator can extract said key counter before it is step advanced, thus obtaining a copy without counting. Such possibility leads to inaccurate copy counting and affects the cost control in office or the fee calculation in the copying service business.
Also the halogen lamp heater is recently employed for heating the fixing roller in a temperature-controlled fixing station, and such lamp heater generates, at the start of power supply, a surge current more than ten times higher than the stationary current. Besides the copier is provided with a direct current power supply for control purpose, having large smoothing condensers. Consequently, upon turning on of the main switch, the surge current in the heater is overlapped with the charging current to said smoothing condensers to generate an overall current which is several ten times higher than the current in the stationary state. Such large current may trigger the circuit breaker for protection, or may reduce the power supply voltage, thus causing undesirable effects on other instruments.
Also the main switch usually have mechanical contacts which inevitably shows bouncing movement at the turning on. The aforementioned surge current during such bouncing movement results in sparking in said contacts, thus causing rapid oxidation of the contacts.
Also the copier is equipped with a lamp for original exposure and heaters for heating fixing rollers for fixing the image onto the transfer sheet. Said fixing rollers are normally composed of a heating roller coming into direct contact with the image on said sheet and a pressure roller for maintaining said sheet in contact with the heating roller. The heating roller is provided with a heater of a capacity generally in the range of 1 kW, while the pressure roller is not provided with heater or is provided with a heater of a smaller capacity for performing auxiliary functions such as for obtaining uniform temperature distribution in the fixing station or increasing the heat capacity. On the other hand, since the receptacles for ordinary use are mostly of a capacity of 15 A for 100 V, it is important to maintain the entire power consumption of the copier below 1.5 kW, as otherwise it cannot be powered from an ordinary receptacle.